The objective of this research is to better define the neural mechanisms which determine the human breathing pattern as a function of respiratory system mechanics separate from the influences of chemical drive. Various aspects of a proposed hierachical model of respiratory control will be experimentally tested: 1) to determine quantitative relationships between respiratory mechanics and both the chemical control of ventilation and the selection of the breathing pattern and the influence of changes in stress and consciousness upon these measures; 3) to determine breathing pattern adaptations to small perturbations of respiratory mechanics from normal; and 4) to evaluate the possible optimal nature of breathing pattern responses to loading both using existing criteria of optimality and using a new criterion based upon the metabolic energy cost of muscular contraction. Different experiments will include: 1) analysis of steady-state responses to loading at fixed levels of alveolar chemistry; 2) statistical assessment of variability and correlation including spectral and cross-correlation analysis techniques; and 3) use of a pseudo-random load application technique designed to facilitate analysis of the responses to small mechanical loads. These experiments will test aspects of the proposed ventilatory control model and will provide information useful to improve this model. The steady-state and breath-by-breath relationships between the breathing pattern components and the respiratory mechanics may help to explain observed correlation between chemical and pattern regulation characteristics. The responses to low-level perturbations of mechanical loads will help to determine the sensitivity of the adaptive control system to loading and these results will be of a value in assessing the importance of mechanical information in determination of the pattern of breathing.